The numbers are: {width}{aspect ratio}{diameter}

A 140/90-15 is a 140 mm wide tire on a 15 inch rim and is 90% tall:wide.

Which, converted to inches, is 5.5" wide and 24.9" outside diameter.

A 140/80-15 tire would again be 5.5" wide, but only 23.8" outside diameter.

In theory.

The Bridgestone wwebsite lists the diameter and width of various Bridgestone 140/90-15 tires, all on a 3.5" wide rim:

S11:  25.0 x 5.8
G544: 25.2 x 6.0
G702: 25.2 x 5.8 s-speed rated
G702: 25.2 x 5.9 h-speed rated
G508: 25.0 x 5.8
G524: 25.3 x 5.6
G536: 25.2 x 5.8

Dunlop lists, for a 140/90-15 tire:

D404: 24.73 x 5.85       (3.5" rim width)
491 Elite II : 25.1 x 5.7 (3.0" rim width)

Dunlop also lists in 140/80-15 on a 3.0" rim:

K555: 24.2 x 5.9

Bottom line: actual tire sizes, width and height, vary between manufacturers, between tire lines from the same manufacturer, between speed ratings for the same model tire, and (not shown but turst me) the rim width the tire is mounted on.

The Dunlop D404 in 140/90 is only a quarter inch larger in radius than the Dunlop K555 in 140/80.  While the Bridgestone 140/90 G524 is over a half inch larger radius.